Long-term shrinkage behaviour of steel-concrete composite slabs with recycled coarse aggregate

Non-uniform shrinkage profile through the slab thickness is observed in composite slabs with natural concrete due to the inability of the slabs to dry from their underside, including an additional deflection for composite slabs under the serviceability state. The porosity and shrinkage deformation of recycled aggregate concrete (RAC) are remarkably increased by the residual mortar adhered to the surface of recycled coarse aggregate (RCA), which will complicate the ability to predict the serviceability of composite slabs with RCA. In this study, two full-scale RAC specimens with depths of 120 mm and 180 mm were prepared and tested for 140 days, with the mid-span and quartiles-span deflections were measured; two small-scale solid concrete samples were poured and measured monitoring the development of non-uniform shrinkage. Results obtained indicated that the non-uniform shrinkage through the slabs depths was approximately linear-distributed, the gradient of which increased with curing time, however, decreased remarkably with the increasing slabs depths. The long-term deflections of two full-scale specimens were remarkably influenced by the non-uniform shrinkage. Based on EC2, a modification of notation size of member (h) was used to predict the shrinkage strain on the top surface of the slabs with one way to diffuse moisture, and the predicted data well match the experimental results.